The present invention relates to a developing device and an image forming apparatus.
An electrophotographic image forming apparatus is configured to form an image through processes of charging, exposure, developing, transferring, fixing and cleaning. There are plural kinds of developing devices for use in the developing process. Among plural kinds of developing devices, a contact-type developing device using a nonmagnetic single-component toner is broadly used, since such a developing device is compact in size and low in cost.
The contact-type developing device using a nonmagnetic single-component toner (hereinafter, simply referred to as a contact-type developing device) includes a photosensitive drum as a latent image bearing body and a developing roller as a developer bearing body. The developing roller contacts the photosensitive drum, and is applied with a voltage to develop a latent image on the photosensitive drum using a toner as a developer. The contact-type developing device further includes a toner layer regulating blade that regulates a thickness of a toner layer formed on the developing roller, and a supply-and-recovery roller that recovers the toner (i.e., a residual toner) that has not used for development from the developing roller, and supplies the recovered toner to the developing roller.
Further, in order to reduce damage to the toner, there is proposed a contact-type developing device in which a brush roller is used as the supply-and-recovery roller (see, Japanese Laid-Open Patent Publication No. 2005-235302).
Generally, in order to ensure printing density, the supply-and-recovery roller is applied with a voltage so as to form an electric field for moving the toner from the supply-and-recovery roller toward the developing roller. Therefore, the supply-and-recovery roller recovers the residual toner from the developing roller only by means of friction between the residual toner and the supply-and-recovery roller, and therefore efficiency in recovering the residual toner is relatively low.
There has been an increasing demand for a technique for enhancing the efficiency in recovering the residual toner from the developing roller.